Subject: Re: [PATCH 08/28] SECURITY: Allow kernel services to override LSM
	settings for task actions [try #2]
From: Stephen Smalley <sds@tycho.nsa.gov>
To: David Howells <dhowells@redhat.com>
Cc: Daniel J Walsh <dwalsh@redhat.com>, casey@schaufler-ca.com,
       linux-kernel@vger.kernel.org, selinux@tycho.nsa.gov,
       linux-security-module@vger.kernel.org
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Organization: National Security Agency
Date: Tue, 15 Jan 2008 09:56:42 -0500
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On Mon, 2008-01-14 at 14:01 +0000, David Howells wrote:
> Stephen Smalley <sds@tycho.nsa.gov> wrote:
> 
> > > 	avc_has_perm(daemon_tsec->sid, nominated_sid,
> > > 		     SECCLASS_CACHE, CACHE__USE_AS_OVERRIDE, NULL);
> > > 
> > > And I assume this doesn't care if one, the other or both of the two SIDs
> > > mentioned are of SECCLASS_PROCESS rather than of SECCLASS_CACHE.
> > 
> > Right, the latter is reasonable.
> 
> Okay...  It looks like I want four security operations/hooks for cachefiles:
> 
>  (1) Check that a daemon can nominate a secid for use by the kernel to override
>      the process subjective secid.
> 
>  (2) Set the secid mentioned in (1).
> 
>  (3) Check that the kernel may create files as a particular secid (this could
>      be specified indirectly by specifying an inode, which would hide the secid
>      inside the LSM).

I don't think this check is on the kernel per se but rather the ability
of the daemon to nominate a secid for use on files created later by the
kernel module.

>  (4) Set the fscreate secid mentioned in (3).
> 
> Now, it's possible to condense (1) and (2) into a single op, and condense (3)
> and (4) into a single op.  That, however, might make the ops unusable by nfsd,
> which may well want to bypass the checks or do them elsewhere.
> 
> Any thoughts?

I think it is fine to combine them.

-- 
Stephen Smalley
National Security Agency

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